1. Technical Field
The invention relates to an interior drum type printer comprising a paper feed mechanism, in which paper to be printed can be fed to the interior surface of a printing drum by means of a paper feeder provided with a deflectable feed roller, a shaft being arranged in the drum center along which a print head can be moved.
2. Background Art
From EP 0 045 788, an inkjet printer is known whose print head is supported to pivot about a shaft. Paper transport to the print head is effected by means of arcuately arranged transport rollers, with the rollers being eliminated in the immediate print head area so that there is the possibility of the paper during printing not being pressed against the drum's cylindrical wall section facing the print head. Line-by-line printing is effected by pivoting the print head about said shaft. Subsequently, the paper is advanced by one line spacing by means of the transport rollers to print the following line in the described manner.
An essential disadvantage of this printer is the sophisticated arrangement and shape of the transport rollers as well as their controlling the paper advance in response to the print head being pivoted. Moreover, the manner in which the transport rollers are positioned does not guarantee that the paper contacts the paper supporting surface in the print head area. Due to differing paper/print head spacing occurring thereby, unsharp print-out is produced. Another disadvantage is that during paper transport a backlash between paper and transport rollers may occur which leads to varying line spacings.
From the journal "Deutscher Drucker", No. 34, Sep. 12, 1991, an interior drum type recorder "Linotronic 630" is known, in which magazined photographic web material that can be unwound and taken up is drawn through a hollow drum by means of a motordriven take-up magazine. During advance, the photographic material is sucked to the interior surface of the drum by applying a vacuum. In the drum center, an advancing system for a light source and related optical means is arranged on a shaft, said system being movable along said shaft. During horizontal movement of the optical system the photographic material is exposed in vertical direction.
Since such apparatus are not intended for printing on paper, the solution is not suitable for interior drum type printers either. For example, sheet paper cannot be printed due to the transport means guiding only continuous paper through the drum. Also, sucking the photographic material to the interior surface of the drum by vacuum is technically too complicated for interior drum type printers and is not effective.